In an article summarizing the study findings, the research team noted that, “the volume of service delivered by a transit agency in a region is by far the largest factor explaining public transit ridership in the North American metropolitan regions we studied.” The researchers first presented their findings at the annual meeting of the Transportation Research Board in Washington, D.C., last January and released the paper earlier this month.

In order to identify the factors that might be contributing to transit ridership, the study team collected data on transit ridership, fares, and operations between 2002-2015 for 25 large transit agencies in the United States and Canada, using data from the National Transit Database and the Canadian Urban Transit Association. They measured operations in terms of vehicle revenue kilometers (VRK) for bus, rail, and both modes combined, which the American Public Transit Association defines as the distance traveled by vehicles available to the public with an expectation of carrying passengers. The researchers then analyzed the relationships between ridership and VRK, as well as more than a dozen additional factors like gasoline prices, geographic and population sizes, GDP per capita, percentage of households without a car, and presence of Uber and bike sharing.

In summarizing the results, the researchers explain that, “the more service a transit authority provides (measured as the number of kilometers driven annually by public transit vehicles—VRK), the more transit trips it will attract.” They found that a 10 percent increase in VRK was associated with a roughly 8 percent increase in ridership, with all other variables constant. Their model also shows a much stronger relationship between bus service volume and ridership than rail service volume and ridership.

While transit service was the largest determinant of ridership—with potential implications for public policy—a number of additional factors may be playing a role. The second largest contributing factor in the study turned out to be car ownership. This finding aligns with other recent research. For example, SSTI wrote recently about a study from the Southern California Association of Governments that found private vehicle ownership to be the largest contributing factor in declining transit ridership in its six California counties (though the researchers also noted that land use patterns in Southern California make it difficult to get around without a car, providing an economic and social incentive to drive).

McGill University’s study also found that transit fares play a significant role in ridership—a 10 percent rise in ticket prices was associated with a 2 percent drop in ridership in their findings. Gas price also had a statistically significant, though much weaker, impact on ridership. The presence of Uber and bike sharing systems, by contrast, did not have a statistically significant impact (though the researchers acknowledge that they did not have data on trip volumes for ride-hailing vehicles or bikeshare, which could make a difference).

One additional factor that may be playing a role is the economic displacement of low-income earners from inner city neighborhoods to first ring suburbs, though that was not studied. Lower-income residents use transit regularly to get to work, grocery stores, and other necessities. By contrast, higher-income residents, while wanting to live close to transit tend not to use it as frequently. As low-income residents are pushed out of the city, they end up in more suburban neighborhoods that discourage bus ridership through dispersed land uses, poor street connectivity, low population densities, and a lack of pedestrian infrastructure. In some of the cities studied, residents most likely to use transit may be facing declining access to it.